Method and apparatus for configuring a long training field in a wireless local area network system

ABSTRACT

Proposed herein is a LTF sequence that is used in a wireless LAN system. The proposed LTF sequence may correspond to a sequence for a second frequency band of a second wireless LAN system. The proposed sequence may be generated through a LTF sequence that is used in a first wireless LAN system, which is different from the second wireless LAN system. The LTF sequence of the first wireless LAN system may correspond to a sequence for a first frequency band, which is different from the second frequency band. A length of an IDFT/DFT period and a bandwidth of a transmission frequency that are applied to the LTF sequence of the first wireless LAN system are different from a length of an IDFT/DFT period and a bandwidth of a transmission frequency that are applied to the LTF sequence of the second wireless LAN system.

CROSS-REFERENCE TO RELATED APPLICATION

The present application for patent claims priority to ProvisionalApplication Nos. 62/199,243 filed on Jul. 31, 2015, 62/201,097 filed onAug. 4, 2015, and 62/210,398 filed on Aug. 26, 2015, which areincorporated herein by reference.

BACKGROUND

Technical Field

The present invention relates to a training signal that is being used ina wireless LAN system and, more particularly, to a method and apparatusfor configuring a Long Training Field (LTF) in a wireless LAN system.

Description of the Related Art

Discussion for a next-generation wireless local area network (WLAN) isin progress. In the next-generation WLAN, an object is to 1) improve aninstitute of electronic and electronics engineers (IEEE) 802.11 physical(PHY) layer and a medium access control (MAC) layer in bands of 2.4 GHzand 5 GHz, 2) increase spectrum efficiency and area throughput, 3)improve performance in actual indoor and outdoor environments such as anenvironment in which an interference source exists, a denseheterogeneous network environment, and an environment in which a highuser load exists, and the like.

An environment which is primarily considered in the next-generation WLANis a dense environment in which access points (APs) and stations (STAs)are a lot and under the dense environment, improvement of the spectrumefficiency and the area throughput is discussed. Further, in thenext-generation WLAN, in addition to the indoor environment, in theoutdoor environment which is not considerably considered in the existingWLAN, substantial performance improvement is concerned.

In detail, scenarios such as wireless office, smart home, stadium,Hotspot, and building/apartment are largely concerned in thenext-generation WLAN and discussion about improvement of systemperformance in a dense environment in which the APs and the STAs are alot is performed based on the corresponding scenarios.

In the next-generation WLAN, improvement of system performance in anoverlapping basic service set (OBSS) environment and improvement ofoutdoor environment performance, and cellular offloading are anticipatedto be actively discussed rather than improvement of single linkperformance in one basic service set (BSS). Directionality of thenext-generation means that the next-generation WLAN gradually has atechnical scope similar to mobile communication. When a situation isconsidered, in which the mobile communication and the WLAN technologyhave been discussed in a small cell and a direct-to-direct (D2D)communication area in recent years, technical and business convergenceof the next-generation WLAN and the mobile communication is predicted tobe further active.

SUMMARY OF THE INVENTION Technical Objects

This specification proposes an enhanced method related to a method andapparatus for configuring a training signal in a transmitting device ina wireless LAN system.

As an example of the present invention, the present invention proposes amethod for transmitting a training signal of a second wireless LANsystem by using a training signal that is being used in a first wirelessLAN system.

Technical Solutions

An example of this specification may be applied to a transmittingapparatus of a wireless LAN system. The transmitting apparatus includesan AP or a non-AP STA.

The example of this specification includes a method for configuring andtransmitting a LTF field.

The method according to this specification includes a step ofconfiguring a long training field (LTF) for a second frequency band of asecond wireless LAN system by using a LTF sequence for a first frequencyband of a first wireless LAN system.

Additionally, the method according to this specification also includes astep of transmitting the LTF for the second frequency band through aPhysical layer Protocol Data Unit (PPDU) including a first field areaand a second field area.

The second field area may include the LTF and a data field for thesecond frequency band.

An IDFT/DFT period being applied to each symbol of the first field areamay be configured to be shorter than an IDFT/DFT period being applied toeach symbol of the second field area.

A bandwidth of the first frequency band may be configured to be largerthan a bandwidth of the second frequency band.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

FIG. 5 is a diagram illustrating a layout of resource units (RUs) usedin a band of 40 MHz.

FIG. 6 is a diagram illustrating a layout of resource units (RUs) usedin a band of 80 MHz.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B accordingto an embodiment.

FIG. 9 illustrates an example of a trigger frame.

FIG. 10 illustrates an example of a common information field.

FIG. 11 illustrates an example of a sub-field being included in a peruser information field.

FIG. 12 is a block diagram illustrating an example of an uplink MU PPDU.

FIG. 13 illustrates a drawing indicating in units of resource units(RUs) a PAPR of a 4× HE-LTF sequence that is being used for a 20 MHztransmission.

FIG. 14 illustrates a drawing indicating in units of resource units(RUs) a PAPR of a 4× HE-LTF sequence that is being used for a 40 MHztransmission.

FIG. 15 illustrates a drawing indicating in units of resource units(RUs) a PAPR of a 4× HE-LTF sequence that is being used for a 80 MHztransmission.

FIG. 16 illustrates another drawing indicating in units of resourceunits (RUs) a PAPR of a 4× HE-LTF sequence that is being used for a 80MHz transmission.

FIG. 17 illustrates a drawing indicating in units of resource units(RUs) a PAPR of a 2× HE-LTF sequence that is being used for a 20 MHztransmission.

FIG. 18 illustrates a drawing indicating in units of resource units(RUs) a PAPR of a 2× HE-LTF sequence that is being used for a 40 MHztransmission.

FIG. 19 illustrates a drawing indicating in units of resource units(RUs) a PAPR of a 2× HE-LTF sequence that is being used for a 80 MHztransmission.

FIG. 20 illustrates another drawing indicating in units of resourceunits (RUs) a PAPR of a 2× HE-LTF sequence that is being used for a 80MHz transmission.

FIG. 21 illustrates a flow chart of a procedure according to an exampleof this specification.

FIG. 22 illustrates a block diagram showing a wireless communicationsystem in which the example of this specification can be applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

An upper part of FIG. 1 illustrates the structure of an infrastructurebasic service set (BSS) of institute of electrical and electronicengineers (IEEE) 802.11.

Referring the upper part of FIG. 1, the wireless LAN system may includeone or more infrastructure BSSs 100 and 105 (hereinafter, referred to asBSS). The BSSs 100 and 105 as a set of an AP and an STA such as anaccess point (AP) 125 and a station (STA1) 100-1 which are successfullysynchronized to communicate with each other are not concepts indicatinga specific region. The BSS 105 may include one or more STAs 105-1 and105-2 which may be joined to one AP 130.

The BSS may include at least one STA, APs providing a distributionservice, and a distribution system (DS) 110 connecting multiple APs.

The distribution system 110 may implement an extended service set (ESS)140 extended by connecting the multiple BSSs 100 and 105. The ESS 140may be used as a term indicating one network configured by connectingone or more APs 125 or 230 through the distribution system 110. The APincluded in one ESS 140 may have the same service set identification(SSID).

A portal 120 may serve as a bridge which connects the wireless LANnetwork (IEEE 802.11) and another network (e.g., 802.X).

In the BSS illustrated in the upper part of FIG. 1, a network betweenthe APs 125 and 130 and a network between the APs 125 and 130 and theSTAs 100-1, 105-1, and 105-2 may be implemented. However, the network isconfigured even between the STAs without the APs 125 and 130 to performcommunication. A network in which the communication is performed byconfiguring the network even between the STAs without the APs 125 and130 is defined as an Ad-Hoc network or an independent basic service set(IBSS).

A lower part of FIG. 1 illustrates a conceptual view illustrating theIBSS.

Referring to the lower part of FIG. 1, the IBSS is a BSS that operatesin an Ad-Hoc mode. Since the IBSS does not include the access point(AP), a centralized management entity that performs a managementfunction at the center does not exist. That is, in the IBSS, STAs 150-1,150-2, 150-3, 155-4, and 155-5 are managed by a distributed manner. Inthe IBSS, all STAs 150-1, 150-2, 150-3, 155-4, and 155-5 may beconstituted by movable STAs and are not permitted to access the DS toconstitute a self-contained network.

The STA as a predetermined functional medium that includes a mediumaccess control (MAC) that follows a regulation of an Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standard and aphysical layer interface for a radio medium may be used as a meaningincluding all of the APs and the non-AP stations (STAs).

The STA may be called various a name such as a mobile terminal, awireless device, a wireless transmit/receive unit (WTRU), user equipment(UE), a mobile station (MS), a mobile subscriber unit, or just a user.

Meanwhile, the term user may be used in diverse meanings, for example,in wireless LAN communication, this term may be used to signify a STAparticipating in uplink MU MIMO and/or uplink OFDMA transmission.However, the meaning of this term will not be limited only to this.

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard. As illustrated in FIG. 2, various types of PHY protocol dataunits (PPDUs) may be used in a standard such as IEEE a/g/n/ac, etc. Indetail, LTF and STF fields include a training signal, SIG-A and SIG-Binclude control information for a receiving station, and a data fieldincludes user data corresponding to a PSDU.

In the embodiment, an improved technique is provided, which isassociated with a signal (alternatively, a control information field)used for the data field of the PPDU. The signal provided in theembodiment may be applied onto high efficiency PPDU (HE PPDU) accordingto an IEEE 802.11ax standard. That is, the signal improved in theembodiment may be HE-SIG-A and/or HE-SIG-B included in the HE PPDU. TheHE-SIG-A and the HE-SIG-B may be represented even as the SIG-A andSIG-B, respectively. However, the improved signal proposed in theembodiment is not particularly limited to an HE-SIG-A and/or HE-SIG-Bstandard and may be applied to control/data fields having various names,which include the control information in a wireless communication systemtransferring the user data.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

The control information field provided in the embodiment may be theHE-SIG-B included in the HE PPDU. The HE PPDU according to FIG. 3 is oneexample of the PPDU for multiple users and only the PPDU for themultiple users may include the HE-SIG-B and the corresponding HE SIG-Bmay be omitted in a PPDU for a single user.

As illustrated in FIG. 3, the HE-PPDU for multiple users (MUs) mayinclude a legacy-short training field (L-STF), a legacy-long trainingfield (L-LTF), a legacy-signal (L-SIG), a high efficiency-signal A(HE-SIG A), a high efficiency-signal-B (HE-SIG B), a highefficiency-short training field (HE-STF), a high efficiency-longtraining field (HE-LTF), a data field (alternatively, an MAC payload),and a packet extension (PE) field. The respective fields may betransmitted during an illustrated time period (that is, 4 or 8 μs).

More detailed description of the respective fields of FIG. 3 will bemade below.

FIG. 4 is a diagram illustrating a layout of resource units (RUs) usedin a band of 20 MHz.

As illustrated in FIG. 4, resource units (RUs) corresponding to tone(that is, subcarriers) of different numbers are used to constitute somefields of the HE-PPDU. For example, the resources may be allocated bythe unit of the RU illustrated with respect to the HE-STF, the HE-LTF,and the data field.

As illustrated in an uppermost part of FIG. 4, 26 units (that is, unitscorresponding to 26 tones). 6 tones may be used as a guard band in aleftmost band of the 20 MHz band and 5 tones may be used as the guardband in a rightmost band of the 20 MHz band. Further, 7 DC tones may beinserted into a center band, that is, a DC band and a 26-unitcorresponding to each 13 tones may be present at left and right sides ofthe DC band. The 26-unit, a 52-unit, and a 106-unit may be allocated toother bands. Each unit may be allocated for a receiving station, thatis, a user.

Meanwhile, the RU layout of FIG. 4 may be used even in a situation for asingle user (SU) in addition to the multiple users (MUs) and in thiscase, as illustrated in a lowermost part of FIG. 4, one 242-unit may beused and in this case, three DC tones may be inserted.

In one example of FIG. 4, RUs having various sizes, that is, a 26-RU, a52-RU, a 106-RU, a 242-RU, and the like are proposed, and as a result,since detailed sizes of the RUs may extend or increase, the embodimentis not limited to a detailed size (that is, the number of correspondingtones) of each RU.

FIG. 5 is a diagram illustrating a layout of resource units (RUs) usedin a band of 40 MHz.

Similarly to a case in which the RUs having various RUs are used in oneexample of FIG. 4, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, and the likemay be used even in one example of FIG. 5. Further, 5 DC tones may beinserted into a center frequency, 12 tones may be used as the guard bandin the leftmost band of the 40 MHz band and 11 tones may be used as theguard band in the rightmost band of the 40 MHz band.

In addition, as illustrated in FIG. 5, when the RU layout is used forthe single user, the 484-RU may be used. That is, the detailed number ofRUs may be modified similarly to one example of FIG. 4.

FIG. 6 is a diagram illustrating a layout of resource units (RUs) usedin a band of 80 MHz.

Similarly to a case in which the RUs having various RUs are used in oneexample of each of FIG. 4 or 5, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU,and the like may be used even in one example of FIG. 6. Further, 7 DCtones may be inserted into the center frequency, 12 tones may be used asthe guard band in the leftmost band of the 80 MHz band and 11 tones maybe used as the guard band in the rightmost band of the 80 MHz band. Inaddition, the 26-RU may be used, which uses 13 tones positioned at eachof left and right sides of the DC band.

Moreover, as illustrated in FIG. 6, when the RU layout is used for thesingle user, 996-RU may be used and in this case, 5 DC tones may beinserted. Meanwhile, the detailed number of RUs may be modifiedsimilarly to one example of each of FIG. 4 or 5.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

A block illustrated in FIG. 7 is another example of describing theHE-PPDU block of FIG. 3 in terms of a frequency.

An illustrated L-STF 700 may include a short training orthogonalfrequency division multiplexing (OFDM) symbol. The L-STF 700 may be usedfor frame detection, automatic gain control (AGC), diversity detection,and coarse frequency/time synchronization.

An L-LTF 710 may include a long training orthogonal frequency divisionmultiplexing (OFDM) symbol. The L-LTF 710 may be used for finefrequency/time synchronization and channel prediction.

An L-SIG 720 may be used for transmitting control information. The L-SIG720 may include information regarding a data rate and a data length.Further, the L-SIG 720 may be repeatedly transmitted. That is, a newformat, in which the L-SIG 720 is repeated (for example, may be referredto as R-LSIG) may be configured.

An HE-SIG-A 730 may include the control information common to thereceiving station.

In detail, the HE-SIG-A 730 may include information on 1) a DL/ULindicator, 2) a BSS color field indicating an identify of a BSS, 3) afield indicating a remaining time of a current TXOP period, 4) abandwidth field indicating at least one of 20, 40, 80, 160 and 80+80MHz, 5) a field indicating an MCS technique applied to the HE-SIG-B, 6)an indication field regarding whether the HE-SIG-B is modulated by adual subcarrier modulation technique for MCS, 7) a field indicating thenumber of symbols used for the HE-SIG-B, 8) a field indicating whetherthe HE-SIG-B is configured for a full bandwidth MIMO transmission, 9) afield indicating the number of symbols of the HE-LTF, 10) a fieldindicating the length of the HE-LTF and a CP length, 11) a fieldindicating whether an OFDM symbol is present for LDPC coding, 12) afield indicating control information regarding packet extension (PE),13) a field indicating information on a CRC field of the HE-SIG-A, andthe like. A detailed field of the HE-SIG-A may be added or partiallyomitted. Further, some fields of the HE-SIG-A may be partially added oromitted in other environments other than a multi-user (MU) environment.

An HE-SIG-B 740 may be included only in the case of the PPDU for themultiple users (MUs) as described above. Principally, an HE-SIG-A 750 oran HE-SIG-B 760 may include resource allocation information(alternatively, virtual resource allocation information) for at leastone receiving STA.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B accordingto an embodiment.

As illustrated in FIG. 8, the HE-SIG-B field includes a common field ata frontmost part and the corresponding common field is separated from afield which follows therebehind to be encoded. That is, as illustratedin FIG. 8, the HE-SIG-B field may include a common field including thecommon control information and a user-specific field includinguser-specific control information. In this case, the common field mayinclude a CRC field corresponding to the common field, and the like andmay be coded to be one BCC block. The user-specific field subsequentthereafter may be coded to be one BCC block including the “user-specificfield” for 2 users and a CRC field corresponding thereto as illustratedin FIG. 8.

A previous field of the HE-SIG-B 740 may be transmitted in a duplicatedform on an MU PPDU. In the case of the HE-SIG-B 740, the HE-SIG-B 740transmitted in some frequency band (e.g., a fourth frequency band) mayeven include control information for a data field corresponding to acorresponding frequency band (that is, the fourth frequency band) and adata field of another frequency band (e.g., a second frequency band)other than the corresponding frequency band. Further, a format may beprovided, in which the HE-SIG-B 740 in a specific frequency band (e.g.,the second frequency band) is duplicated with the HE-SIG-B 740 ofanother frequency band (e.g., the fourth frequency band). Alternatively,the HE-SIG B 740 may be transmitted in an encoded form on alltransmission resources. A field after the HE-SIG B 740 may includeindividual information for respective receiving STAs receiving the PPDU.

The HE-STF 750 may be used for improving automatic gain controlestimation in a multiple input multiple output (MIMO) environment or anOFDMA environment.

The HE-LTF 760 may be used for estimating a channel in the MIMOenvironment or the OFDMA environment.

The size of fast Fourier transform (FFT)/inverse fast Fourier transform(IFFT) applied to the HE-STF 750 and the field after the HE-STF 750, andthe size of the FFT/IFFT applied to the field before the HE-STF 750 maybe different from each other. For example, the size of the FFT/IFFTapplied to the HE-STF 750 and the field after the HE-STF 750 may be fourtimes larger than the size of the FFT/IFFT applied to the field beforethe HE-STF 750.

For example, when at least one field of the L-STF 700, the L-LTF 710,the L-SIG 720, the HE-SIG-A 730, and the HE-SIG-B 740 on the PPDU ofFIG. 7 is referred to as a first field, at least one of the data field770, the HE-STF 750, and the HE-LTF 760 may be referred to as a secondfield. The first field may include a field associated with a legacysystem and the second field may include a field associated with an HEsystem. In this case, the fast Fourier transform (FFT) size and theinverse fast Fourier transform (IFFT) size may be defined as a sizewhich is N (N is a natural number, e.g., N=1, 2, and 4) times largerthan the FFT/IFFT size used in the legacy wireless LAN system. That is,the FFT/IFFT having the size may be applied, which is N (=4) timeslarger than the first field of the HE PPDU. For example, 256 FFT/IFFTmay be applied to a bandwidth of 20 MHz, 512 FFT/IFFT may be applied toa bandwidth of 40 MHz, 1024 FFT/IFFT may be applied to a bandwidth of 80MHz, and 2048 FFT/IFFT may be applied to a bandwidth of continuous 160MHz or discontinuous 160 MHz.

In other words, a subcarrier space/subcarrier spacing may have a sizewhich is 1/N times (N is the natural number, e.g., N=4, the subcarrierspacing is set to 78.125 kHz) the subcarrier space used in the legacywireless LAN system. That is, subcarrier spacing having a size of 312.5kHz, which is legacy subcarrier spacing may be applied to the firstfield of the HE PPDU and a subcarrier space having a size of 78.125 kHzmay be applied to the second field of the HE PPDU.

Alternatively, an IDFT/DFT period applied to each symbol of the firstfield may be expressed to be N (=4) times shorter than the IDFT/DFTperiod applied to each data symbol of the second field. That is, theIDFT/DFT length applied to each symbol of the first field of the HE PPDUmay be expressed as 3.2 μs and the IDFT/DFT length applied to eachsymbol of the second field of the HE PPDU may be expressed as 3.2 μs*4(=12.8 μs). The length of the OFDM symbol may be a value acquired byadding the length of a guard interval (GI) to the IDFT/DFT length. Thelength of the GI may have various values such as 0.4 μs, 0.8 μs, 1.6 μs,2.4 μs, and 3.2 μs.

For simplicity in the description, in FIG. 7, it is expressed that afrequency band used by the first field and a frequency band used by thesecond field accurately coincide with each other, but both frequencybands may not completely coincide with each other, in actual. Forexample, a primary band of the first field (L-STF, L-LTF, L-SIG,HE-SIG-A, and HE-SIG-B) corresponding to the first frequency band may bethe same as the most portions of a frequency band of the second field(HE-STF, HE-LTF, and Data), but boundary surfaces of the respectivefrequency bands may not coincide with each other. As illustrated inFIGS. 4 to 6, since multiple null subcarriers, DC tones, guard tones,and the like are inserted during arranging the RUs, it may be difficultto accurately adjust the boundary surfaces.

The user (e.g., a receiving station) may receive the HE-SIG-A 730 andmay be instructed to receive the downlink PPDU based on the HE-SIG-A730. In this case, the STA may perform decoding based on the FFT sizechanged from the HE-STF 750 and the field after the HE-STF 750. On thecontrary, when the STA may not be instructed to receive the downlinkPPDU based on the HE-SIG-A 730, the STA may stop the decoding andconfigure a network allocation vector (NAV). A cyclic prefix (CP) of theHE-STF 750 may have a larger size than the CP of another field and theduring the CP period, the STA may perform the decoding for the downlinkPPDU by changing the FFT size.

Hereinafter, in the embodiment of the present invention, data(alternatively, or a frame) which the AP transmits to the STA may beexpressed as a terms called downlink data (alternatively, a downlinkframe) and data (alternatively, a frame) which the STA transmits to theAP may be expressed as a term called uplink data (alternatively, anuplink frame). Further, transmission from the AP to the STA may beexpressed as downlink transmission and transmission from the STA to theAP may be expressed as a term called uplink transmission.

In addition, a PHY protocol data unit (PPDU), a frame, and datatransmitted through the downlink transmission may be expressed as termssuch as a downlink PPDU, a downlink frame, and downlink data,respectively. The PPDU may be a data unit including a PPDU header and aphysical layer service data unit (PSDU) (alternatively, a MAC protocoldata unit (MPDU)). The PPDU header may include a PHY header and a PHYpreamble and the PSDU (alternatively, MPDU) may include the frame orindicate the frame (alternatively, an information unit of the MAC layer)or be a data unit indicating the frame. The PHY header may be expressedas a physical layer convergence protocol (PLCP) header as another termand the PHY preamble may be expressed as a PLCP preamble as anotherterm.

Further, a PPDU, a frame, and data transmitted through the uplinktransmission may be expressed as terms such as an uplink PPDU, an uplinkframe, and uplink data, respectively.

In the wireless LAN system to which the embodiment of the presentdescription is applied, the whole bandwidth may be used for downlinktransmission to one STA and uplink transmission to one STA. Further, inthe wireless LAN system to which the embodiment of the presentdescription is applied, the AP may perform downlink (DL) multi-user (MU)transmission based on multiple input multiple output (MU MIMO) and thetransmission may be expressed as a term called DL MU MIMO transmission.

In addition, in the wireless LAN system according to the embodiment, anorthogonal frequency division multiple access (OFDMA) based transmissionmethod is preferably supported for the uplink transmission and/ordownlink transmission. That is, data units (e.g., RUs) corresponding todifferent frequency resources are allocated to the user to performuplink/downlink communication. In detail, in the wireless LAN systemaccording to the embodiment, the AP may perform the DL MU transmissionbased on the OFDMA and the transmission may be expressed as a termcalled DL MU OFDMA transmission. When the DL MU OFDMA transmission isperformed, the AP may transmit the downlink data (alternatively, thedownlink frame and the downlink PPDU) to the plurality of respectiveSTAs through the plurality of respective frequency resources on anoverlapped time resource. The plurality of frequency resources may be aplurality of subbands (alternatively, sub channels) or a plurality ofresource units (RUs). The DL MU OFDMA transmission may be used togetherwith the DL MU MIMO transmission. For example, the DL MU MIMOtransmission based on a plurality of space-time streams (alternatively,spatial streams) may be performed on a specific subband (alternatively,sub channel) allocated for the DL MU OFDMA transmission.

Further, in the wireless LAN system according to the embodiment, uplinkmulti-user (UL MU) transmission in which the plurality of STAs transmitsdata to the AP on the same time resource may be supported. Uplinktransmission on the overlapped time resource by the plurality ofrespective STAs may be performed on a frequency domain or a spatialdomain.

When the uplink transmission by the plurality of respective STAs isperformed on the frequency domain, different frequency resources may beallocated to the plurality of respective STAs as uplink transmissionresources based on the OFDMA. The different frequency resources may bedifferent subbands (alternatively, sub channels) or different resourcesunits (RUs). The plurality of respective STAs may transmit uplink datato the AP through different frequency resources. The transmission methodthrough the different frequency resources may be expressed as a termcalled a UL MU OFDMA transmission method.

When the uplink transmission by the plurality of respective STAs isperformed on the spatial domain, different time-space streams(alternatively, spatial streams) may be allocated to the plurality ofrespective STAs and the plurality of respective STAs may transmit theuplink data to the AP through the different time-space streams. Thetransmission method through the different spatial streams may beexpressed as a term called a UL MU MIMO transmission method.

The UL MU OFDMA transmission and the UL MU MIMO transmission may be usedtogether with each other. For example, the UL MU MIMO transmission basedon the plurality of space-time streams (alternatively, spatial streams)may be performed on a specific subband (alternatively, sub channel)allocated for the UL MU OFDMA transmission.

In the legacy wireless LAN system which does not support the MU OFDMAtransmission, a multi-channel allocation method is used for allocating awider bandwidth (e.g., a 20 MHz excess bandwidth) to one terminal. Whena channel unit is 20 MHz, multiple channels may include a plurality of20 MHz-channels. In the multi-channel allocation method, a primarychannel rule is used to allocate the wider bandwidth to the terminal.When the primary channel rule is used, there is a limit for allocatingthe wider bandwidth to the terminal. In detail, according to the primarychannel rule, when a secondary channel adjacent to a primary channel isused in an overlapped BSS (OBSS) and is thus busy, the STA may useremaining channels other than the primary channel. Therefore, since theSTA may transmit the frame only to the primary channel, the STA receivesa limit for transmission of the frame through the multiple channels.That is, in the legacy wireless LAN system, the primary channel ruleused for allocating the multiple channels may be a large limit inobtaining a high throughput by operating the wider bandwidth in acurrent wireless LAN environment in which the OBSS is not small.

In order to solve the problem, in the embodiment, a wireless LAN systemis disclosed, which supports the OFDMA technology. That is, the OFDMAtechnique may be applied to at least one of downlink and uplink.Further, the MU-MIMO technique may be additionally applied to at leastone of downlink and uplink. When the OFDMA technique is used, themultiple channels may be simultaneously used by not one terminal butmultiple terminals without the limit by the primary channel rule.Therefore, the wider bandwidth may be operated to improve efficiency ofoperating a wireless resource.

As described above, when the uplink transmission by the plurality ofrespective STAs (e.g., non-AP STAs) is performed on the frequencydomain, the AP may allocate the different frequency resources to theplurality of respective STAs as the uplink transmission resources basedon the OFDMA. Further, as described above, the different frequencyresources may be different subbands (alternatively, sub channels) ordifferent resources units (RUs).

The different frequency resources are indicated through a trigger framewith respect to the plurality of respective STAs.

FIG. 9 illustrates an example of a trigger frame. The trigger frame ofFIG. 9 allocates resources for Uplink Multiple-User (MU) transmissionand may be transmitted from the AP. The trigger frame may be configuredas a MAC frame and may be included in the PPDU. For example, the triggerframe may be transmitted through the PPDU shown in FIG. 3, through thelegacy PPDU shown in FIG. 2, or through a certain PPDU, which is newlydesigned for the corresponding trigger frame. In case the trigger frameis transmitted through the PPDU of FIG. 3, the trigger frame may beincluded in the data field shown in the drawing.

Each of the fields shown in FIG. 9 may be partially omitted, or otherfields may be added. Moreover, the length of each field may be varieddifferently as shown in the drawing.

A Frame Control field 910 shown in FIG. 9 may include informationrelated to a version of the MAC protocol and other additional controlinformation, and a Duration field 920 may include time information forconfiguring a NAV or information related to an identifier (e.g., AID) ofthe user equipment.

Additionally, a RA field 930 may include address information of areceiving STA of the corresponding trigger frame, and this field mayalso be omitted as required. A TA field 940 may include addressinformation of the STA (e.g., AP) transmitting the corresponding triggerframe, and a common information field 950 may include common controlinformation that is applied to the receiving STA receiving thecorresponding trigger frame.

FIG. 10 illustrates an example of a common information field. Among thesub-fields of FIG. 10, some may be omitted, and other additionalsub-fields may also be added. Additionally, the length of each of thesub-fields shown in the drawing may be varied.

As shown in the drawing, the Length field 1010 may be given that samevalue as the Length field of the L-SIG field of the uplink PPDU, whichis transmitted with respect to the corresponding trigger frame, and theLength field of the L-SIG field of the uplink PPDU indicates the lengthof the uplink PPDU. As a result, the Length field 1010 of the triggerframe may be used for indicating the length of its respective uplinkPPDU.

Additionally, a Cascade Indicator field 1020 indicates whether or not acascade operation is performed. The cascade operation refers to adownlink MU transmission and an uplink MU transmission being performedsimultaneously within the same TXOP. More specifically, this refers to acase when a downlink MU transmission is first performed, and, then,after a predetermined period of time (e.g., SIFS), an uplink MUtransmission is performed. During the cascade operation, only onetransmitting device performing downlink communication (e.g., AP) mayexist, and multiple transmitting devices performing uplink communication(e.g., non-AP) may exist.

A CS Request field 1030 indicates whether or not the status or NAV of awireless medium is required to be considered in a situation where areceiving device that has received the corresponding trigger frametransmits the respective uplink PPDU.

A HE-SIG-A information field 1040 may include information controllingthe content of a SIG-A field (i.e., HE-SIG-A field) of an uplink PPDU,which is being transmitted with respect to the corresponding triggerframe.

A CP and LTF type field 1050 may include information on a LTF length anda CP length of the uplink PPDU being transmitted with respect to thecorresponding trigger frame. A trigger type field 1060 may indicate apurpose for which the corresponding trigger frame is being used, e.g.,general triggering, triggering for beamforming, and so on, a request fora Block ACK/NACK, and so on.

Meanwhile, the remaining description on FIG. 9 will be additionallyprovided as described below.

It is preferable that the trigger frame includes per user informationfields 960#1 to 960#N corresponding to the number of receiving STAsreceiving the trigger frame of FIG. 9. The per user information fieldmay also be referred to as a “RU Allocation field”.

Additionally, the trigger frame of FIG. 9 may include a Padding field970 and a Sequence field 980.

It is preferable that each of the per user information fields 960#1 to960#N shown in FIG. 9 further includes multiple sub-fields.

FIG. 11 illustrates an example of a sub-field being included in a peruser information field. Among the sub-fields of FIG. 11, some may beomitted, and other additional sub-fields may also be added.Additionally, the length of each of the sub-fields shown in the drawingmay be varied.

A User Identifier field 1110 indicates an identifier of an STA (i.e.,receiving STA) to which the per user information corresponds, and anexample of the identifier may correspond to all or part of the AID.

Additionally, a RU Allocation field 1120 may be included in thesub-field of the per user information field. More specifically, in casea receiving STA, which is identified by the User Identifier field 1110,transmits an uplink PPDU with respect to the trigger frame of FIG. 9,the corresponding uplink PPDU is transmitted through the RU, which isindicated by the RU Allocation field 1120. In this case, it ispreferable that the RU that is being indicated by the RU Allocationfield 1120 corresponds to the RU shown in FIG. 4, FIG. 5, and FIG. 6.

The sub-field of FIG. 11 may include a Coding Type field 1130. TheCoding Type field 1130 may indicate a coding type of the uplink PPDUbeing transmitted with respect to the trigger frame of FIG. 9. Forexample, in case BBC coding is applied to the uplink PPDU, the CodingType field 1130 may be set to ‘1’, and, in case LDPC coding is appliedto the uplink PPDU, the Coding Type field 1130 may be set to ‘0’.

Additionally, the sub-field of FIG. 11 may include a MCS field 1140. TheMCS field 1140 may indicate a MCS scheme being applied to the uplinkPPDU that is transmitted with respect to the trigger frame of FIG. 9.

FIG. 12 is a block diagram illustrating an example of an uplink MU PPDU.The uplink MU PPDU of FIG. 12 may be transmitted with respect to theabove-described trigger frame.

As shown in the drawing, the PPDU of FIG. 12 includes diverse fields,and the fields included herein respectively correspond to the fieldsshown in FIG. 2, FIG. 3, and FIG. 7. Meanwhile, as shown in the drawing,the uplink PPDU of FIG. 12 may not include a HE-SIG-B field and may onlyinclude a HE-SIG-A field.

In the related art wireless LAN system, the P matrix (or orthogonalmapping matrix) that is being applied to the LTF field has been definedas described below.

More specifically, in the 802.11ac system, residual carrier frequencyoffset (CFO) is measured by using a pilot. More specifically, residualCFO may be measured by allocating the same pilot to the same tone (orsubcarrier) for each symbol, by configuring the same coefficient, and bymeasuring a phase difference in the pilot values between the symbols.

Additionally, the channel estimation is carried out in the VHT-LTF, andorthogonality between the symbols of the same subcarrier and the streamsis created by multiplying a P matrix, and, then, the channel may bemeasured by using the orthogonality. The P matrix may represent a matrixhaving orthogonality for each row configuring the corresponding matrix.

In this case, the number of LTF fields and the total number of spatialstreams (i.e., space-time streams) may be defined as the relationshipshown below in Table 1.

TABLE 1 Number of streams 1 2 3 4 5 6 7 8 Number of 1 2 4 4 6 6 8 8 LTFs

Meanwhile, the P matrix may be defined as different matrices inaccordance with the total number of space-time streams, and the detailedformat of the matrix may be as described below. More specifically, ifthe total number of space-time streams is equal to or less than 4,Equation 1 is used, and, if the total number of space-time streams isequal to 5 or 6, Equation 2 is used, and, if the total number ofspace-time streams is equal to 7 or 8, Equation 3 is used.

$\begin{matrix}{P_{4 \times 4} = \begin{bmatrix}1 & {- 1} & 1 & 1 \\1 & 1 & {- 1} & 1 \\1 & 1 & 1 & {- 1} \\{- 1} & 1 & 1 & 1\end{bmatrix}} & {\langle{{Equation}\mspace{14mu} 1}\rangle} \\{{P_{6 \times 6} = \begin{bmatrix}1 & {- 1} & 1 & 1 & 1 & {- 1} \\1 & {- w^{1}} & w^{2} & w^{3} & w^{4} & {- w^{5}} \\1 & {- w^{2}} & w^{4} & w^{6} & w^{8} & {- w^{10}} \\1 & {- w^{3}} & w^{6} & w^{9} & w^{12} & {- w^{15}} \\1 & {- w^{4}} & w^{8} & w^{12} & w^{16} & {- w^{20}} \\1 & {- w^{5}} & w^{10} & w^{15} & w^{20} & {- w^{25}}\end{bmatrix}}{where}{w = {\exp ( {{- {j2\pi}}/6} )}}} & {\langle{{Equation}\mspace{14mu} 2}\rangle} \\{P_{8 \times 8} = \begin{bmatrix}P_{4 \times 4} & P_{4 \times 4} \\P_{4 \times 4} & {- P_{4 \times 4}}\end{bmatrix}} & {\langle{{Equation}\mspace{14mu} 3}\rangle}\end{matrix}$

For example, in the IEEE 802.11ac system, in case Equation 1 is used inorder to configure the VHT-LTF field, a method in which i) a first LTFsymbol of a first space-time stream is multiplied by “1”, a second LTFsymbol is multiplied by “−1”, and the remaining two LTF symbols aremultiplied by “1”, ii) first, second, and fourth LTF symbols of a secondspace-time stream are multiplied by “1”, and a third LTF symbol ismultiplied by “−1”, iii) first, second, and third LTF symbols of a thirdspace-time stream are multiplied by “1”, and a fourth LTF symbol ismultiplied by “−1”, and iv) second, third, and fourth LTF symbols of afourth space-time stream are multiplied by “1”, and a first LTF symbolis multiplied by “−1”, may be used.

More specifically, the LTF sequence by which the P matrix is multipliedis defined as a binary sequence that is shown below.

More specifically, LTF_left and LTF_right sequences are defined as shownbelow.

LTF_left={1, 1, −1, −1, 1, 1, −1, 1, −, 1, 1, 1, 1, 1, 1, −1, −1, 1, 1,−1, 1, −1, 1, 1, 1, 1}  <Equation 4>

LTF_right={1, −1, −1, 1, 1, −1, 1, −1, 1, −1, −1, −1, −1, −1, 1, 1, −1,−1, 1, −1, 1, −1, 1, 1, 1,1}  <Equation 5>

In the VHT system, a VHT-LTF sequence for a 20 MHz transmission isdefined as shown below.

VHTLTF_20(−28,28)={1, 1, LTF_left, 0, LTF_right, −1, −1}  <Equation 6>

More specifically, the frequency band for the 20 MHz transmissioncorresponds to frequency indexes “−28” to “28”, and, as shown inEquation 6, the frequency band is defined as the LTF_left and LTF_rightsequences, additional binary values, and a DC value “0”.

In the VHT system, a VHT-LTF sequence for a 40 MHz transmission isdefined as shown below.

VHTLTF_40(−58,58)={LTF_left, 1, LTF_right, −1, −1, −1, 1, 0, 0, 0, −1,1, 1, −1, LTF_left, 1, LTF_right}  <Equation 7>

More specifically, the frequency band for the 40 MHz transmissioncorresponds to frequency indexes “−58” to “58”, and, as shown inEquation 7, the frequency band is defined as the LTF_left and LTF_rightsequences, additional binary values, and a DC value “0”.

In the VHT system, a VHT-LTF sequence for a 40 MHz transmission isdefined as shown below.

In the VHT system, a VHT-LTF sequence for a 80 MHz transmission isdefined as shown below.

VHTLTF_80(−122,122)={LTF_left, 1, LTF_right, −1, −1, −1, 1, 1, −1, 1,−1, 1, 1, −1, LTF_left, 1, LTF_right, 1, −1, 1, −1, 0, 0, 0, 1, −1, −1,1, LTF_left, 1, LTF_right, −1, −1, −1, 1, 1, −1, 1, −1, 1, 1, −1,LTF_left, 1, LTF_right}  <Equation 8>

More specifically, the frequency band for the 80 MHz transmissioncorresponds to frequency indexes “−122” to “122”, and, as shown inEquation 8, the frequency band is defined as the LTF_left and LTF_rightsequences, additional binary values, and a DC value “0”.

In the VHT system, a VHT-LTF sequence for a 160 MHz transmission isdefined as shown below.

VHTLTF_160(−250,250)={VHTLTF(−122,122), 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,VHTLTF(−122,122)}  <Equation 9>

More specifically, the frequency band for the 160 MHz transmissioncorresponds to frequency indexes “−250” to “250”, and, as shown inEquation 9, the frequency band is defined as a structure of repeatingthe VHT-LTF sequence for the 80 MHz transmission.

In the following example, an example of the above-described Equation 4to Equation 9 may be re-used for the HE-LTF sequence. In this case, theVHT-LTF sequence that is being re-used may correspond to a sequencehaving a gamma value applied thereto or may correspond to a sequence nothaving a gamma value applied thereto. For example, in the VHT system,for a decrease in PAPR of a STF or LTF, an operation of rotating a toneby using an orthogonal sequence, such as {1, j}, {1, −1}, and so on, maybe performed. Hereinafter, the sequences VHTLTF_20, VHTLTF_40,VHTLTF_80, VHTLTF_160, and so on, which are being applied to thefollowing equations, may each correspond to a sequence having a gammavalue applied thereto or a sequence not having a gamma value appliedthereto.

Hereinafter, in this specification, a HELTF sequence that is availablefor usage in a HE PPDU will be proposed. As shown in FIG. 7, and so on,not only 1×FFT but also 2×FFT or 4×FFT may be applied to a HE-LTF 760.More specifically, as compared to a legacy field of the HE PPDU, aFFT/IFFT having a size that is 2 or 4 times larger may be applied, and,accordingly, the subcarrier spacing may be ½ times or ¼ times thesubcarrier spacing that was used in the conventional wireless LANsystem.

More specifically, an IEEE802.11ax system or a HEW system may use aHE-LTF having a length that is 2 times or 4 times longer for eachbandwidth as compared with the conventional 11ac system or VHT system.In the following specification, a method of designing a HE-LTF sequenceby re-using the VHT-LTF sequence of the conventional 11ac system as muchas possible will be proposed.

Example (1)—4× HE-LTF

Hereinafter, an example of a 4× HE-LTF will be proposed. Morespecifically, Example (1), which will hereinafter be described indetail, proposes diverse types of LTF sequences for the 20 MHz, 40 MHz,and 80 MHz transmissions.

1-A) 20 MHz

In case of the 4× HE LTF, as compared to the VHT LTF, since the size ofthe FFT block being applied herein has been increased to a size that is4 times larger, even if a HE LTF for a 20 MHz transmission is used, theVHT LTF for a 80 MHz transmission may be re-used.

More specifically, the VHT LTF sequence for the 80 MHz transmissioncorresponds to frequency indexes “−122” to “122”, and since this willthe same for the 4× HE LTF for the 20 MHz transmission, the 4× HE LTFsequence for the 20 MHz transmission may be defined as the equationshown below.

HELTF_4×,20(−122:1:122)=VHTLTF_80(−122:1:122)   <Equation 10>

In the equation, “(−122:1:122)” signifies that a sequence is beinginserted at a frequency index interval of “1” starting from frequencyindex “−122” to frequency index “122”. Additionally, “VHTLTF_80”signifies a VHTLTF sequence for a 80 MHz transmission, and “HELTF_4×,20”signifies 4× HELTF among the HELTF sequences for the 20 MHztransmission. The above-described indication method may be identicallyapplied to the equations shown below.

As shown below, this example may be modified by using a method ofinserting a DC index and a sequence element “0” in each of the left andright indexes of the DC index. additionally, the VHTLTF sequence mayalso be multiplied by C1 and C2 values. Each of the C1 and C2 valuesmay, for example, respectively correspond to BPSK values (i.e., “1” and“−1”) and may be optimized based on the PAPR. Additionally, in thefollowing equation, the positions of VHTLTF_80(−122:1:−2) andVHTLTF_80(2:1:122) may vary and may be optimized with respect to thePAPR. In this case, the length of the HELTF sequence being configured oneach of the left side and the right side with respect to the DC indexmay each be equal to 121.

HELTF_4×,20(−122:1:122)={c1*VHTLTF_80(−122:1:−2), 0, 0, 0,c2*VHTLTF_80(2:1:122)}  <Equation 11>

Meanwhile, among the HELTF sequences, a sequence corresponding to a leftside area of the DC index (i.e., an area corresponding to a frequencyindex having a negative number) is referred to as a negative sequence,and a sequence corresponding to a right side area of the DC index (i.e.,an area corresponding to a frequency index having a positive number) isreferred to as a positive sequence.

1-B) 40 MHz

The length respective to each of the negative and positive sequences forHELTF_4×,40 may each be equal to 242. In this case, the HELTF_4×,20 (orVHTLTF_80) may be repeated twice, so as to configure HELTF_4×,40. Therespective example is shown below in detail.

HELTF_4×,40(−244:1:244)={c1*VHTLTF_4×,20(−122:1:−2),c2*VHTLTF_4×,20(2:1:122), 0, 0, 0, 0, 0, c3*VHTLTF_4×,20(−122:1:−2),c4*VHTLTF_4×,20(2:1:122)}  <Equation 12>

The fact that each of C1 to C4 may correspond to a BPSK value (i.e., “1”and “−1”) and that each of C1 to C4 may be optimized based on the PAPRis the same as the above-described example. Additionally, the fact thatthe detailed positions of VHTLTF_4×,20(−122:1:−2) andVHTLTF_4×,20(2:1:122) may be varied and that the detailed positions maybe optimized based on the PAPR is also the same as the above-describedexample.

1-C) 80 MHz

The length respective to each of the negative and positive sequences forHELTF_4×,80 may each be equal to 498. In this case, the HELTF_4×,20 (orVHTLTF_80) may be repeated four times, so as to configure HELTF_4×,80.Additionally, 14 extra values may be used herein. The respective exampleis shown below in detail.

HELTF_4×,80(−500:1:500)={c1*VHTLTF_4×,20(−122:1:−2),c2*VHTLTF_4×,20(2:1:122), c3*VHTLTF_4×,20(−122:1:−2),c4*VHTLTF_4×,20(2:1:122), a1, a2, . . . , a14, 0, 0, 0, 0, 0, a15, a16,. . . , a28, c5*VHTLTF_4×,20(−122:1:−2), c6*VHTLTF_4×,20(2:1:122),c7*VHTLTF_4×,20(−122:1:−2), c8*VHTLTF_4×,20(2:1:122)}  <Equation 13>

The fact that each of C1 to C8 may correspond to a BPSK value (i.e., “1”and “−1”) and that each of C1 to C8 may be optimized based on the PAPRis the same as the above-described example. The fact that the detailedpositions of VHTLTF_4×,20(−122:1:−2), VHTLTF_4×,20(2:1:122), and a1 toa28 may be varied and that the detailed positions may be optimized basedon the PAPR is also the same as the above-described example. Suchdetailed exemplary modification is as shown below. More specifically, itwill be preferable to design the sequence based on left-and-rightorthogonality.

HELTF_4×,80(−500:1:500)={c1*VHTLTF_4×,20(−122:1:−2),c2*VHTLTF_4×,20(2:1:122), a1, a2, c3*VHTLTF_4×,20(−122:1:−2),c4*VHTLTF_4×,20(2:1:122), a3, a4, . . . , a14, 0, 0, 0, 0, 0, a15, a16,. . . , a26, c5*VHTLTF_4×,20(−122:1:−2), c6*VHTLTF_4×,20(2:1:122), a27,a28, c7*VHTLTF_4×,20(−122:1:−2), c8*VHTLTF_4×,20(2:1:122)}  <Equation14>

Moreover, the modification shown below is also possible. Morespecifically, the following configuration may be made by using oneBarker sequence having a length of 13 (marked as B13) and one extravalue on each side. The 13-length Barker sequence that is being insertedon each of the left side and right side of the center frequency isdefined as shown below in Equation 16.

HELTF_4×,80(−500:1:500)={c1*VHTLTF_4×,20(−122:1:−2),c2*VHTLTF_4×,20(2:1:122), c3*VHTLTF_4×,20(−122:1:−2),c4*VHTLTF_4×,20(2:1:122), c5*B13, a1, 0, 0, 0, 0, 0, a2, c6*B13,c7*VHTLTF_4×,20(−122:1:−2), c8*VHTLTF_4×,20(2:1:122),c9*VHTLTF_4×,20(−122:1:−2), c10*VHTLTF_4×,20(2:1:122)}  <Equation 15>

B13={1, 1, 1, 1, 1, −1, −1, 1, 1, −1, 1, −1, 1}  <Equation 16>

The fact that the detailed positions of VHTLTF_4×,20(−122:1:−2) andVHTLTF_4×,20(2:1:122) may be varied, and that the element of the B13sequence may also be changed, and that the positions of a1/a2 may alsobe changed is the same as the above-described example, and suchpositions may be optimized based on the PAPR.

1-D) 160 MHz

For the 160 MHz transmission, the HELTF_4×,80 may be repeated two times.The respective example is shown below in detail.

HELTF_4×,160={HELTF_4×,80, HELTF_4×,80}  <Equation 17>

Example (2)—2× HE-LTF

Hereinafter, an example of a 2× HE-LTF will be proposed. Morespecifically, Example (2), which will hereinafter be described indetail, proposes diverse types of LTF sequences for the 20 MHz, 40 MHz,and 80 MHz transmissions.

2-A) 20 MHz

The length respective to each of the negative and positive sequences forHELTF_2×,20 may each be equal to 61. In this case, 61 units may be taken(or cut out) from each of the left/right sides of the HELTF_4×,20 (orVHTLTF_80) and may then be used. A detailed example of the HELTF_2×,20is as shown below.

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−62), 0,c2*VHTLTF_4×,20(62:1:122)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−62), 0,c2*VHTLTF_4×,20(2:1:62)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−62:1:−2), 0,c2*VHTLTF_4×,20(2:1:62)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−62:1:−2), 0,c2*VHTLTF_4×,20(62:1:122)}  <Equation 18>

Among the sequences indicated in Equation 18, which is presented above,any one of the sequences may be used. Alternatively, as shown in thefollowing Equation, by using the sequence on only one of the left/rightsides, a sequence for the 20 MHz transmission may be configured.

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−62), 0,c2*VHTLTF_4×,20(−62:1:−2)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−62:1:−2), 0,c2*VHTLTF_4×,20(−122:1:−62)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(62:1:122), 0,c2*VHTLTF_4×,20(2:1:62)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(2:1:62), 0,c2*VHTLTF_4×,20(62:1:122)}  <Equation 19>

Among the sequences indicated in Equation 19, which is presented above,any one of the sequences may be used. Alternatively, as shown in thefollowing Equation, by using the sequence on only one of the left/rightsides and by inserting at least one extra value (indicated as “a”), asequence for the 20 MHz transmission may be configured.

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−62), 0,c2*VHTLTF_4×,20(−61:1:−2), a}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−62), 0, a,c2*VHTLTF_4×,20(−61:1:−2)}

HELTF_2×,20(−122:2:122)={a, c1*VHTLTF_4×,20(−122:1:−63), 0,c2*VHTLTF_4×,20(−62:1:−2)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−63), a, 0,c2*VHTLTF_4×,20(−62:1:−2)}  <Equation 20>

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(2:1:62), 0,c2*VHTLTF_4×,20(63:1:122), a}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(2:1:62), 0, a,c2*VHTLTF_4×,20(63:1:122)}

HELTF_2×,20(−122:2:122)={a, c1*VHTLTF_4×,20(2:1:61), 0,c2*VHTLTF_4×,20(62: 1:122)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(2:1:61), a, 0,c2*VHTLTF_4×,20(62: 1:122)}  <Equation 21>

Among the sequences indicated in Equation 20 and Equation 21, which arepresented above, any one of the sequences may be used. Alternatively, asshown in the following Equation, by selecting the length of the sequenceon only one of the left/right sides as 60 or 61 and by inserting atleast one extra value (indicated as “a”), a sequence for the 20 MHztransmission may be configured.

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−63), a, 0,c2*VHTLTF_4×,20(62:1:122)}

HELTF_2×,20(−122:2:122)={a, c1*VHTLTF_4×,20(−122:1:−63), 0,c2*VHTLTF_4×,20(62: 1:122)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−61:1:−2), a, 0,c2*VHTLTF_4×,20(62: 1:122)}

HELTF_2×,20(−122:2:122)={a, c1*VHTLTF_4×,20(−61:1:−2), 0,c2*VHTLTF_4×,20(62: 1:122)}  <Equation 22>

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−63), a, 0,c2*VHTLTF_4×,20(2: 1:62)}

HELTF_2×,20(−122:2:122)={a, c1*VHTLTF_4×,20(−122:1:−63), 0,c2*VHTLTF_4×,20(2: 1:62)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−61:1:−2), a, 0,c2*VHTLTF_4×,20(2:1:62)}

HELTF_2×,20(−122:2:122)={a, c1*VHTLTF_4×,20(−61:1:−2), 0,c2*VHTLTF_4×,20(2:1:62)}  <Equation 23>

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−62), 0, a,c2*VHTLTF_4×,20(2:1:61)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−62), 0,c2*VHTLTF_4×,20(2:1:61), a}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−62), 0, a,c2*VHTLTF_4×,20(63:1:122)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−62), 0,c2*VHTLTF_4×,20(63:1:122), a}  <Equation 24>

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−62:1:−2), 0, a,c2*VHTLTF_4×,20(2:1:61)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−62:1:−2), 0,c2*VHTLTF_4×,20(2:1:61), a}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−62:1:−2), 0, a,c2*VHTLTF_4×,20(63:1:122)}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−62:1:−2), 0,c2*VHTLTF_4×,20(63:1:122), a}  <Equation 25>

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−63), a1, 0, a2,c2*VHTLTF_4×,20(63:1:122)}

HELTF_2×,20(−122:2:122)={a1, c1*VHTLTF_4×,20(−122:1:−63), 0,c2*VHTLTF_4×,20(63:1:122), a2}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−122:1:−63), a1, 0, a2,c2*VHTLTF_4×,20(2:1:61)}

HELTF_2×,20(−122:2:122)={a1, c1*VHTLTF_4×,20(−122:1:−63), 0,c2*VHTLTF_4×,20(2:1:61), a2}  <Equation 26>

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−61:1:−2), a1, 0, a2,c2*VHTLTF_4×,20(63:1:122)}

HELTF_2×,20(−122:2:122)={a1, c1*VHTLTF_4×,20(−61:1:−2), 0,c2*VHTLTF_4×,20(63:1:122), a2}

HELTF_2×,20(−122:2:122)={c1*VHTLTF_4×,20(−61:1:−2), a1, 0, a2,c2*VHTLTF_4×,20(2:1:61)}

HELTF_2×,20(−122:2:122)={a1, c1*VHTLTF_4×,20(−61:1:−2), 0,c2*VHTLTF_4×,20(2:1:61), a2}  <Equation 27>

Just as in the above-described Example (1), the values of c1, c2, and soon, in the equations presented above may be configured as BPSK values,and the positions of a sequence part having the length of 60 to 61 andextra values (a1, a2), and so on, may be changed (or varied), and thepositions may be optimized based on the PAPR.

2-B) 40 MHz

The sequence length of HELTF_2×,40 may be equal to 242. In this case,the sequence may be configured by using the HELTF_4×,20 (or VHTLTF_80)once. The respective example is shown below in detail.

HELTF_2×,40(−244:2:244)=HELTF_4×,20(−122:1:122)   <Equation 28>

Alternatively, as shown below, a sequence having an additionalarithmetic calculation applied thereto may be used.

HELTF_2×,40(−244:2:244)={c1*VHTLTF_4×,20(−122:1:−2), 0, 0, 0,c2*VHTLTF_4×,20(2:1:122)}  <Equation 29>

Just as in the above-described Example (1), the values of c1, c2, and soon, in the equations presented above may be configured as BPSK values,and the positions of VHTLTF_4×,20(−122:1:−2) and VHTLT_F4×,20(2:1:122)may be changed (or varied), and the positions may be optimized based onthe PAPR.

2-C) 80 MHz

The negative and positive sequence lengths of HELTF_2×,80 may each beequal to 249. Accordingly, the sequence for a 80 MHz transmission may beconfigured by using the HELTF_4×,20 (or VHTLTF_80) twice. A detailedexample of HELTF_2×,80 is as shown below.

HELTF_2×,80(−500:2:500)={c1*VHTLTF_4×,20(−122:1:−2),c2*VHTLTF_4×,20(2:1:122), a1, a2, . . . , a7, 0, 0, 0, a8, a9, . . . ,a14, c3*VHTLTF_4×,20(−122:1:−2), c4*VHTLTF_4×,20(2:1:122}  <Equation 30>

Alternatively, instead of the seven (7) extra values on each side (a1 toa7 or a8 to a14), a Barker sequence having a length of 7 (marked as B7)may be used. A detailed example is as shown below.

HELTF_2×,80(−500:2:500)={c1*VHTLTF_4×,20(−122:1:−2),c2*VHTLTF_4×,20(2:1:122), c3*B7, 0, 0, 0, c4*B7,c5*VHTLTF_4×,20(−122:1:−2), c6*VHTLTF_4×,20(2:1:122}  <Equation 31>

B7={1, 1, 1, −1, −1, 1, −1}  <Equation 32>

Just as in the above-described Example (1), the values of c1, c2, and soon, in the equations presented above may be configured as BPSK values,and the positions of the inserted sequences or the positions of theextra values may be changed (or varied), and the positions may beoptimized based on the PAPR.

2-D) 160 MHz

An example of configuring a sequence for a 160 MHz transmission byrepeating HELTF_2×,80 twice is proposed herein.

HELTF_2×,160={HELTF_2×,80, HELTF_2×,80}  <Equation 33>

A PAPR performance respective to a sequence according to theabove-described method will hereinafter be described in detail. Morespecifically, the PAPR respective to the 4× HE-LTF sequence, which isindicated in Equation 34 to Equation 36 shown below, will be describedin detail. The VHTLTF_80 that is indicated in Equation 34 shown belowmay correspond to a sequence having a gamma value of a VHT wireless LANsystem applied thereto.

HELTF_4×,20(−122:1:122)=VHTLTF_80(−122:1:122)   <Equation 34>

An example of a sequence for a 40 MHz transmission is configured byusing a method of repeating part of the sequence shown in Equation 34,and the corresponding example is as shown below.

HELTF_4×,40(−244:1:244)={HELTF_left, HELTF_right, 0, 0, 0, 0, 0,HELTF_left, −HELTFright},

HELTF_left=HELTF_4×,20(−122:1:−2)

HELTF_right=HELTF_4×,20(2:1:122)   <Equation 35>

An example of the sequence for a 80 MHz transmission is configured asthe equation shown below by using a sequence part of Equation 34 and aBarker Sequence having a length of 13 (indicated as B13).

HELTF_4×,80(−500:1:500)={HELTF_left, HELTF_right, −HELTF_left,HELTF_right, −B13, 1, 0, 0, 0, 0, 0, −1, B13, −HELTF_left, −HELTF_right,−HELTF_left, HELTF_right},

B13={1, 1, 1, 1, 1, −1, −1, 1, 1, −1, 1, −1, 1}  <Equation 36>

FIG. 13 illustrates a drawing indicating in units of resource units(RUs) a PAPR of a 4× HE-LTF sequence that is being used for a 20 MHztransmission. Each block of FIG. 13 corresponds to a RU for the 20 MHztransmission shown in FIG. 4. The PAPR indicated in FIG. 13 indicates aPAPR of the sequence of Equation 34.

FIG. 14 illustrates a drawing indicating in units of resource units(RUs) a PAPR of a 4× HE-LTF sequence that is being used for a 40 MHztransmission. Each block of FIG. 14 corresponds to a RU for the 40 MHztransmission shown in FIG. 5. The PAPR indicated in FIG. 14 indicates aPAPR of the sequence of Equation 35.

FIG. 15 and FIG. 16 illustrate drawings indicating in units of resourceunits (RUs) a PAPR of a 4× HE-LTF sequence that is being used for a 80MHz transmission. Each block of FIG. 15 and FIG. 16 corresponds to a RUfor the 80 MHz transmission shown in FIG. 6. More specifically, FIG. 15illustrates a left-side band of the center frequency, and FIG. 16illustrates a right-side band of the center frequency. The PAPRindicated in FIG. 15 and FIG. 16 indicates a PAPR of the sequence ofEquation 36.

The PAPR respective to center 26-RU is omitted from FIG. 15 and FIG. 16,and, more specifically, the PAPR is calculated as 4.52. Additionally,the PAPR respective to the entire band is calculated as 5.85.

Hereinafter, the PAPR respective to the 2× HE-LTF sequence, which isindicated in Equation 37 to Equation 39 shown below, will be describedin detail. An example of Equation 37 shown below is configured for a 20MHz transmission, and the example presented herein uses part ofHELTF_left and HELTF_right, which are described in Equation 35.

HELTF_2×,20(−122:2:122)={HELTF_left(61:1:121), 0,HELTF_right(1:1:61)}  <Equation 37>

An example of the sequence for a 40 MHz transmission uses HELTF_left andHELTF_right, which are described in the description of Equation 35, andthe exemplary sequence is as shown below in the following equation.

HELTF_2×,40(−244:2:244)={HELTF_left, 0, 0, 0, HELTF_right}  <Equation38>

An example of the sequence for a 80 MHz transmission is configured asthe equation shown below by using HELTF_left and HELTF_right, which aredescribed in Equation 35, and a Barker Sequence having a length of 7(indicated as B7).

HELTF_2×,80(−500:2:500)={HELTF_left, HELTF_right, B7, 0, 0, 0, B7,HELTF_left, −HELTFright},   <Equation 39>

B7={1, 1, 1, −1, −1, 1, −1}

FIG. 17 illustrates a drawing indicating in units of resource units(RUs) a PAPR of a 2× HE-LTF sequence that is being used for a 20 MHztransmission. Each block of FIG. 17 corresponds to a RU for the 20 MHztransmission shown in FIG. 4. The PAPR indicated in FIG. 17 indicates aPAPR of the sequence of Equation 37.

FIG. 18 illustrates a drawing indicating in units of resource units(RUs) a PAPR of a 2× HE-LTF sequence that is being used for a 40 MHztransmission. Each block of FIG. 18 corresponds to a RU for the 40 MHztransmission shown in FIG. 5. The PAPR indicated in FIG. 18 indicates aPAPR of the sequence of Equation 38.

FIG. 19 and FIG. 20 illustrate drawings indicating in units of resourceunits (RUs) a PAPR of a 2× HE-LTF sequence that is being used for a 80MHz transmission. Each block of FIG. 19 and FIG. 20 corresponds to a RUfor the 80 MHz transmission shown in FIG. 6. More specifically, FIG. 19illustrates a left-side band of the center frequency, and FIG. 20illustrates a right-side band of the center frequency. The PAPRindicated in FIG. 19 and FIG. 20 indicates a PAPR of the sequence ofEquation 39.

The PAPR respective to center 26-RU is omitted from FIG. 19 and FIG. 20,and, more specifically, the PAPR is calculated as 4.39. Additionally,the PAPR respective to the entire band is calculated as 5.86.

FIG. 21 illustrates a flow chart of a procedure according to an exampleof this specification.

An example of this specification relates to a sequence for two differentwireless LAN systems. For example, a second wireless LAN system maysignify a HEW system or an IEEE 802.11ax system, and a first wirelessLAN system may signify a VHT system or an IEEE 802.11ax system.

More specifically, as shown in step S2110, in a transmitting device, along training field (LTF) sequence for a second frequency band of asecond wireless LAN system by using a LTF sequence for a first frequencyband of a first wireless LAN system. The transmitting device maycorrespond to an AP or a non-AP STA. Herein, for example, the firstfrequency band may signify a 80 MHz band, and a second frequency bandmay signify a 20 MHz or 40 MHz band. For example, a long training field(LTF) sequence for the first frequency band of the first wireless LANsystem may correspond to a VHTLTF_80 sequence, and a LTF for the secondfrequency band of the second wireless LAN system may correspond toHELTF_4×, 20 or HELTF_4×, 40. Additionally, a specific sequence maycorrespond to any one of the equations presented in the above-describedexample of the present invention.

As shown in step S2120, the transmitting device may transmit a LTF forthe second frequency band through a Physical layer Protocol Data Unit(PPDU), which includes a first field area and a second field area. ThePPDU may include all or any part of the fields shown in FIG. 7. Thesecond field area may include a STF, a LTF, and a data field, and thefirst field area may include all or any part of the fields before theSTF.

FIG. 22 illustrates a block diagram showing a wireless communicationsystem in which the example of this specification can be applied.

Referring to FIG. 22, as a station (STA) that can realize theabove-described exemplary embodiment, the wireless device may correspondto an AP or a non-AP station (non-AP STA). The wireless device maycorrespond to the above0described user or may correspond to atransmitting device transmitting a signal to the user.

The AP 2200 includes a processor 2210, a memory 2220, and a radiofrequency unit (RF unit) 2230.

The RF unit 2230 is connected to the processor 2210, thereby beingcapable of transmitting and/or receiving radio signals.

The processor 2210 implements the functions, processes, and/or methodsproposed in this specification. For example, the processor 2210 may berealized to perform the operations according to the above-describedexemplary embodiments of the present invention. More specifically, theprocessor 2210 may perform the operations that can be performed by theAP, among the operations that are disclosed in the exemplary embodimentsof FIG. 1 to FIG. 21.

The non-AP STA 2250 includes a processor 2260, a memory 2270, and aradio frequency unit (RF unit) 2280.

The RF unit 2280 is connected to the processor 2260, thereby beingcapable of transmitting and/or receiving radio signals.

The processor 2260 may implement the functions, processes, and/ormethods proposed in the exemplary embodiment of the present invention.For example, the processor 2260 may be realized to perform the non-APSTA operations according to the above-described exemplary embodiments ofthe present invention. The processor may perform the operations of thenon-AP STA, which are disclosed in the exemplary embodiments of FIG. 1to FIG. 21.

The processor 2210 and 2260 may include an application-specificintegrated circuit (ASIC), another chip set, a logical circuit, a dataprocessing device, and/or a converter converting a baseband signal and aradio signal to and from one another. The memory 2220 and 2270 mayinclude a read-only memory (ROM), a random access memory (RAM), a flashmemory, a memory card, a storage medium, and/or another storage device.The RF unit 2230 and 2280 may include one or more antennas transmittingand/or receiving radio signals.

When the exemplary embodiment is implemented as software, theabove-described method may be implemented as a module (process,function, and so on) performing the above-described functions. Themodule may be stored in the memory 2220 and 2270 and may be executed bythe processor 2210 and 2260. The memory 2220 and 2270 may be locatedinside or outside of the processor 2210 and 2260 and may be connected tothe processor 2210 and 2260 through a diversity of well-known means.

As described above, the method and apparatus for configuring a LongTraining Field (LTF) in a wireless LAN system have the followingadvantages.

A method according to an example of this specification proposes anexample of configuring a LTF sequence of a new wireless LAN system byusing a LTF sequence that is being used in another wireless LAN system.

According to an exemplary of this specification, the present inventionhas an advantageous effect of decreasing the level of complexity indesigning a LTF sequence in a new system.

Although the aforementioned exemplary system has been described on thebasis of a flowchart in which steps or blocks are listed in sequence,the steps of the present invention are not limited to a certain order.Therefore, a certain step may be performed in a different step or in adifferent order or concurrently with respect to that described above.Further, it will be understood by those ordinary skilled in the art thatthe steps of the flowcharts are not exclusive. Rather, another step maybe included therein or one or more steps may be deleted within the scopeof the present invention.

What is claimed is:
 1. A method for configuring a Long Training Field(LTF) in a wireless LAN system, comprising: configuring, by atransmitting apparatus, a LTF for a second frequency band of a secondwireless LAN system by using a LTF sequence for a first frequency bandof a first wireless LAN system; and transmitting, by the transmittingapparatus, the LTF for the second frequency band through a Physicallayer Protocol Data Unit (PPDU) including a first field area and asecond field area, wherein the second field area includes the LTF and adata field for the second frequency band, wherein an IDFT/DFT periodbeing applied to each symbol of the first field area is shorter than anIDFT/DFT period being applied to each symbol of the second field area,and wherein a bandwidth of the first frequency band is larger than abandwidth of the second frequency band.
 2. The method of claim 1,wherein the LTF sequence for the first frequency band corresponds to aVery High Throughput (VHT) LTF sequence, wherein the LTF for the secondfrequency band corresponds to a High Efficiency (HE) LTF, and whereinthe PPDU corresponds to a HE PPDU.
 3. The method of claim 1, wherein thebandwidth of the first frequency band is equal to 80 MHz, and whereinthe bandwidth of the second frequency band is equal to 20 MHz.
 4. Themethod of claim 1, wherein the IDFT/DFT period being applied to eachsymbol of the first field area is 2 times or 4 times shorter than theIDFT/DFT period being applied to each symbol of the second field area.5. The method of claim 1, wherein, in case the IDFT/DFT period beingapplied to each symbol of the first field area is 4 times shorter thanthe IDFT/DFT period being applied to each symbol of the second fieldarea, and in case the bandwidth of the first frequency band is equal to80 MHz and the bandwidth of the second frequency band is equal to 20MHz, the LTF for the second frequency band is configured by using a LTFsequence for the first frequency band.
 6. The method of claim 5,wherein, in case the IDFT/DFT period being applied to each symbol of thefirst field area is 4 times shorter than the IDFT/DFT period beingapplied to each symbol of the second field area, and in case thebandwidth of the first frequency band is equal to 80 MHz and thebandwidth of the second frequency band is equal to 40 MHz, the LTF forthe second frequency band is configured by repeating the LTF sequencefor the first frequency band.
 7. A transmitting apparatus forconfiguring a Long Training Field (LTF) in a wireless LAN system,comprising: a radio frequency unit (RF unit) configured to transmit orreceive radio signals; and a processor configured to control the RFunit, wherein the processor: configures a LTF for a second frequencyband of a second wireless LAN system by using a LTF sequence for a firstfrequency band of a first wireless LAN system, and transmits the LTF forthe second frequency band through a Physical layer Protocol Data Unit(PPDU) including a first field area and a second field area, wherein thesecond field area includes the LTF and a data field for the secondfrequency band, wherein an IDFT/DFT period being applied to each symbolof the first field area is shorter than an IDFT/DFT period being appliedto each symbol of the second field area, and wherein a bandwidth of thefirst frequency band is larger than a bandwidth of the second frequencyband.